One pigtailed macaque that was a product of inbreeding (part of another project no longer) developed an unusual multifocal cutaneous T-cell lymphoma. Diagnostic samples showed this macaque to be negative for a panel of viruses, including Herpes, SIV, CMBV, SRV-1, SRV-5, and STLV-1. However, it is known that a subset of human cases of mycosis fungoides and adult T-cell lymphoma (ATL) are HTLV-1 negative. To test the hypothesis that the condition of this macaque is due to a yet unknown infectious agent, blood was collected at the time of necropsy and transfused to two nave macaques. Blood subsequently collected from these two macaques has been distributed for clinical monitoring (complete blood counts, lymphocyte subset analysis, and serum chemistries) and virological analysis. This work is still in progress. Both macaques remain in apparent good health. FUNDING NIH grant RR00166.